Replacement or reduction of chemical fungicides has been achieved through the use of biologically based fungicides, an approach falling within the definition of Biological Control as proposed by Cook and Baker (1983): “Biological control is the reduction of the amount of inoculum or disease-producing activity of a pathogen accomplished by or through one or more organism other than man”. This broad definition includes use of less virulent variants of the pathogen, more resistant cultivars of the host, and microbial antagonists “that interfere with the survival or disease-producing activities of the pathogen”.
A more complex evaluation of the environmental interactions is required to use such Biocontrol Agents (BCAs). In fact environmental conditions affect not only the survival of BCAs, but also their efficacy against pathogens (Paulitz, 2000). BCAs that are more flexible in terms of environmental adaptation can be more easily developed into commercial products, as their applications and target markets can be wider than those of BCAs requiring specific environmental conditions.
The selection of antagonistic Trichoderma strains with enhanced tolerance to unfavorable environmental conditions can increase the reliability of Trichoderma-based biocontrol programs (Kredics et al., 2000). It is also important to note that the most effective BCAs for use against plant pathogens are those that have better stress tolerance than their target pathogens (Kredics et al., 2000; 2004). Trichoderma is a cosmopolitan genus, which can colonize soils, rhizospheres and phyllospheres. Trichoderma species are frequently found on decaying wood and vegetable material. Several Trichoderma strains are economically important producers of industrial enzymes.
Trichoderma strains have been already used as biocontrol agents against numerous plant pathogens and quite a few have been developed for use as commercial (i.e Trichoderma harzianum, known as Trichodex®) biocontrol products for field and greenhouse crops (Elad, 2000; Harman, 2000).
However a great variability exists in terms of biocontrol activity, specificity, mechanism of action, production of metabolites and survival in soil or on plant among Trichoderma species, which affect their use as BCAs (Benitez et al., 2004). Moreover there are still several important pathologies, such as those caused by the Armillaria genus on grapevine for which fully effective biocontrol agents have neither been isolated nor characterized.